In conventional planters, seed sensors are employed to detect the passage of seed through the seed tube. There are various types of sensors suitable for detecting seeds passing through a seed tube, but the most common sensor is a photoelectric or optical sensor, such as the type distributed by Dickey-John Corporation of Auburn, Ill. As disclosed in U.S. Pat. No. 7,152,540 (“the '540 patent”), incorporated herein by reference, photoelectric seed sensors generally include a light source element and a light receiving element or detector disposed over apertures in the forward and rearward walls of the seed tube. When a seed passes between the light source and the detector, the seed interrupts the light beam. When the light beam is interrupted a signal pulse is generated indicating the passage of a seed. The generated signal pulse is communicated to the planter monitor (not shown). The planter monitor counts the signal pulses for purposes of determining seed count or population as well as monitoring the time between signal pulses for purposes of determining seed spacing. In addition to determining seed count and seed spacing, if the time interval between generated signal pulses exceeds a predefined time period, the monitor is typically configured to provide an audible and/or visual alarm to indicate to the operator that there is a problem with the particular row unit, such as the seed hopper running empty or a malfunction of the seed meter or the sensor.
In conventional planters the seed sensors are mounted near the midpoint of the seed tube to protect the sensor from damage during planting operations as well as to minimize ambient light, dust and particulate matter interfering with the light beam. However, it is well known that by the time the seeds pass through the seed tube before being deposited into the seed furrow, the actual in-furrow seed-to-seed spacing can vary dramatically from the seed-to-seed spacing detected by the seed sensor at the midpoint of the seed tube. This is due to the fact that no matter how uniformly spaced the seed meter may dispense sequential seeds into the seed tube, seed ricochet within the seed tube as the seed passes through the tube can significantly affect the velocities of the seeds as they exit the tube.
Seed ricochet off the sidewalls of the seed tube may be caused by the seed not entering the seed tube at the proper location, or due to irregularities or obstructions along the path of travel of the seed within the seed tube, or due to changes in vertical accelerations caused by the row unit encountering dirt clods, crop residue, rocks or changes in terrain as the planter traverses the field. If one seed ricochets more or less than an adjacent seed as it passes through the seed tube, it can result in significant irregularities or differences in the spatial placement between adjacent seeds within the furrow. For example, if one seed ricochets off the sidewalls of the seed tube three times before exiting the seed tube versus a seed that does not ricochet at all, or a seed that only ricochets once or twice, seeds experiencing more ricochet will exit the seed tube at a slower velocity than those experiencing fewer ricochets. This difference in seed velocity upon exiting the seed tube results in inconsistent seed-to-seed spacing in the furrow.
Thus, to more accurately reflect the actual in-furrow seed-to-seed placement, ideally the seed sensor should be placed at or near the bottom of the seed tube. However, for the reasons identified above, an optical sensor would be rendered non-functional if it was positioned at or near the end of the seed tube because the ambient light, dust and particulate matter would interfere with the light beam. Accordingly, there is a need for a seed sensor that can be mounted at or near the bottom or egress end of the seed tube and which can withstand the environmental conditions at such a location while still accurately detecting the passage of seeds as they exit or are about to exit the seed tube.